The present invention relates generally to a signal demodulator, and more particularly, the present invention relates to a system to perform angle quantization using log division.
Angle Quantization (AQ) is a function that is widely used on many communication hardware demodulators. A basic summary of the field is that plain radio waves of a particular frequency, called carrier waves, are manipulated to carry useful information, such as sound, digital data, or pictures. To do so, a transmitter changes the carrier waves in some way that corresponds to the information, and a receiver has to detect the changes to recover the information. Changing the carrier to put information into the signal is called modulation. Getting the information out at the receiver is called detection or demodulation.
One modulation technique is to transmit the information in the phase of a signal. This is called phase shift keying. Here, an angle quantizer is utilized to examine an incoming signal and determine the phase of that signal. Once the phase has been determined, the desired information can be retrieved or calculated.
Prior art systems utilized electronic circuits to analyze the inputs of a signal to determine its phase. The circuit shown in FIG. 1 is an example of such a circuit. The inputs to the circuits are considered and labeled as I and Q, which represent coordinates in a Cartesian Coordinate System. The input I represents the real component of a signal and the input Q represents the imaginary component of a signal. Once the coordinates are plotted, a line can be drawn to the origin permitting a measurement of the angle between the line and the axis. This angle is considered the phase of the signal and the plotting of the I and Q inputs is called phase mapping. Thus, the output of the entire circuit is the phase of a signal.
Conventional signal demodulators performing angle quantization utilize a ROM lookup table to perform the step of an I/Q division and the arc tangent phase mapping. Because the I/Q division was being performed within the ROM, the sizes of the ROMs become necessarily enormous. The ROM sizes could be measured by 2{circumflex over ( )}(2Xxe2x88x924), where X is the number of phase mapping. It is therefore desirable to reduce the amount of hardware that is required to perform angle quantization as the bit widths increase.
According to a preferred embodiment of the invention, a system to perform angle quantization comprises: a log ROM lookup table to provide a log of a real input of a signal and a log of an imaginary input of the signal, a subtractor to subtract the log of the real input from the log of the imaginary input to provide a division, and a ROM lookup table to calculate a phase of the division.